pidfs: remove unused members from struct pidfs_inode
We've moved persistent information to struct pid.
So there's no need for these anymore.
Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-6-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>